(1) Field of the Invention
The present invention relates to an assist-air type fuel injection method and device in a fuel-injection type internal combustion engine for an automobile and so on in which an assist-air is supplied toward an injected fuel so as to promote atomization of fuel injected from a fuel injection valve.
(2) Related Art
In a fuel injection type internal combustion engine, there have been generalized, in order to improve idling stability and transition response through improvement in combustibility, those provided with an assist-air type fuel injection device in which an assist-air is supplied toward a fuel injected from a fuel injection valve to an intake system so as to promote atomization of the fuel for improved atomization and mixing performance of the fuel and sucked air (See Japanese Unexamined U.M. Publication No. 1-85462).
In this kind of fuel injection type internal combustion engine, a fuel injection amount is controlled by controlling an injection period (injection pulse width) and regulating fuel injection pressure from the fuel injection valve with a pressure regulator.
Therefore, an intake pressure is introduced as a signal pressure from a collector part of the intake system and so on to a signal pressure chamber of the pressure regulator to keep the fuel pressure supplied to the fuel injection valve at a pressure higher than the above intake pressure by a constant differential pressure, by which the fuel is injected and supplied (See Japanese Unexamined Patent Publication No. 63-275863).
However, with such a conventional pressure regulating method, with regard to those in which the assist-air is supplied to the injected fuel as mentioned above, the pressure at a nozzle part of the fuel injection valve is higher than the intake pressure of the intake system, and an injection flow rate is restrained by an influence of the supply pressure of the above assist-air, whereby the fuel injection amount is diminished from a control amount.
That is, when the pulse width of an injection signal applied to the fuel injection valve is sequentially increased in the state where supply of the assist-air is stopped, the injection flow rate of the fuel is increased in proportion to the pulse width as shown by a characteristic line 24 shown by the two-dot and dashes line in FIG. 4. However, when the assist-air is supplied, the injection flow rate is lowered because it is affected by this air pressure as shown by a characteristic line 25 shown by the solid line.